1. Field of the Invention
The present invention relates to a vortex pump used, for example, as an air pump in an internal combustion engine.
2. Description of the Related Art
Japanese Unexamined Utility Model Publication No. 55-41531 discloses a vortex pump as an air pump utilized for an internal combustion engine for reducing an amount of toxic emissions in an exhaust gas therefrom.
This kind of vortex pump is provided with a housing, and a cover connected to the housing such that an annular vortex chamber is formed between the housing and the casing. An impeller is constructed by a disk on a drive shaft connected to a rotating motor, an annular blade support portion integral with the outer end of disk member, and two rows of angular blades along the entire circumference of the support portion, which blades are integral with the support portion. The blades are located in the vortex chamber and cause a forced flow of fluid to be introduced into the vortex chamber, which is then forced out therefrom. The housing and the casing have a pair of opposite annular projections extending axially toward each other such that an annular space is formed between the opposed projections. The disk portion of the impeller is located such that it passes radially through the annular space, whereby the disk portion is connected to the blade support portion at a location radially outside of the annular projected portions, to thus create a seal constructed by a pair of axial slits formed between the annular projection of the housing and the disk portion, and the annular projection of the cover and the disk portion, a pair of axial slits formed between the support portion and the housing, and the support portion and the cover, and a pair of radial slits formed between the support portion and the housing, and the support portion and the cover. These inner and outer pairs of the axial slits are connected to each other via the respective radial slits.
In such a construction of the seal, an inwardly directed flow of leak fluid from the vortex chamber occurs via the outer axial slits, the radial slits, and then the inner axial slits. Namely, a steep change through an angle of 90 degrees in the direction of the flow of the leak flow occurs not only at the location at which the outer pair of the axial slits are connected to the radial slits, but also at the location at which the radial slits are connected to the inner pair of the axial slits. Such a steep change in the direction of the flow of the leak fluid allows the leak resistance value of the fluid to be increased, whereby an effective seal effect can be obtained without increasing the length of the seal.
In this type of vortex pump, to obtain an effective sealing effect, the thicknesses of these outer axial slits, intermediate radial slits, and inner axial slits should be kept as small as possible, but in this connection, upon assembling, it is inevitable that the disk portion of the impeller be connected to the drive shaft under a condition such that the disk member is more or less inclined with respect to the shaft. Such an inclined assembly of the disk portion of the impeller to the drive shaft causes the impeller to come into contact with the housing or the cover when the thicknesses of the slits are small. Therefore, the value of the thicknesses of the slits has been made a relatively large value, so that no contact of the parts via these slits occurs even when the disk member is connected to the drive shaft under an inclined condition, and thus the sealing ability is inevitably worsened.
In such a kind of vortex pump, to obtain a desired effective sealing ability, it is possible to elongate the lengths of these slits while keeping the thicknesses of the slits as small as possible, such that any contact between the impeller and the housing or cover is prevented even when the impeller disk portion is obliquely connected to the shaft. This solution of an increased length of the slits is disadvantageous in that there will be a corresponding increase in a rotating momentum of the impeller. Furthermore, an increase of the length of the radial slits may cause the axial thickness of the disk portion to be decreased, to thereby lower the mechanical strength of the disk portion when it is subjected to a centrifugal force during a high speed rotation of the impeller.